132 FRAGMENTS OF SCIENCE. 
sity as the creatures swung to and fro between the surface 
and the deeper water. Foam, at a certain depth below 
the surface, was also green. In a rough sea the light 
which penetrated the summit of a wave sometimes 
reached the eye, a beautiful green cap being thus placed 
upon the wave, even in indigo water. 
But how is this color to be connected with the suspended 
particles? Thus. Take the dinner-plate which showed so 
brilliant a green when thrown into indigo water. Suppose 
it to diminish in size, until it reaches an almost micro- 
scopic magnitude. It would still behave substantially as 
the larger plate, sending to the eye its modicum of green 
light. If the plate, instead of being a large coherent mass, 
were ground to a powder sufficiently fine, and in this con- 
dition diffused through the clear sea-water, it would also 
send green light to the eye. In fact, the suspended par- 
ticles which the home examination reveals, act in all 
essential particulars like the plate, or like the screw-blades, 
or like the foam, or like the bellies of the porpoises. Thus 
I think the greenness of the sea is physically connected 
with the matter which it holds in suspension. 
We reached Portsmouth on January 5, 1871. Then 
ended a voyage which, though its main object was not 
realized, has left behind it pleasant memories, both of the 
aspects of nature and the kindliness of men. 
CHAPTER VII. 
NIAGARA.* 
IT is one of the disadvantages of reading books about 
natural scenery that they fill the mind with pictures, often 
exaggerated, often distorted, often blurred, and, even 
when well drawn, injurious to the freshness of first im- 
pressions. Such has been the fate of most of us with re- 
gard to the Falls of Niagara. There was little accuracy in 
the estimates of the first observers of the cataract. Startled 
by an exhibition of power so novel and so grand, emotion 
* A Discourse delivered at the Royal Institution of Great Britain, 
April 4, 1873. 
